The effect of seed layers on the giant magnetoresistance (GMR) response of bottom spin-filter spin valves (SFSVs) of the structure (seed layer)/PtMn/CoFe/Cu/CoFe/NiFe/Cu/Ta have been studied in detail. Four types of seed layers, NiFeCr, Ta/NiFeCr, NiFeCr/NiFe, and Ta/NiFe were used. The GMR response has been found to be very sensitive to the type and the thickness of the seed layers, which determine the crystallographic quality of the films and the degree of the fcc to fct phase transformation of the PtMn crystals in the films. Among the four, Ta/NiFeCr and NiFeCr/NiFe seed layers give the optimal GMR performance at a NiFeCr layer thickness of about 40–45 Å.
Exosomes, nanovesicles derived from cells, contain a variety of biomolecules that can be considered biomarkers for disease diagnosis, including microRNAs (miRNAs). Given knowledge and demand, inexpensive, robust, and easy-to-use tools that are compatible with downstream nucleic acid detection should be developed to replace traditional methodologies for point-of-care testing (POCT) applications. This study deploys a paper-based extraction kit for exosome and exosomal miRNA analytical system with some quantifying methods to serve as an easy sample preparation for a possible POCT process. Exosomes concentrated from HCT116 cell cultures were arrested on paper-based immunoaffinity devices, which were produced by immobilizing anti-CD63 antibodies on Whatman filter paper, before being subjected to paper-based silica devices for nucleic acids to be trapped by silica nanoparticles adsorbed onto Whatman filter paper. Concentrations of captured exosomes were quantified by enzyme-linked immunosorbent assay (ELISA), demonstrating that paper-based immunoaffinity devices succeeded in capturing and determining exosome levels from cells cultured in both neutral and acidic microenvironments, whereas microRNA 21 (miR-21), a biomarker for various types of cancers and among the nucleic acids absorbed onto the silica devices, was determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR) to prove that paper-based silica devices were capable of trapping exosomal nucleic acids. The developed paper-based kit and the devised procedure was successfully exploited to isolate exosomes and exosomal nucleic acids from different biological samples (platelet-poor plasma and lesion fluid) as clinical applications.
FeCo films and their lamination with ultrathin NiFe layers down to 5 Å were deposited using dc magnetron sputtering techniques. Soft magnetic FeCo films were obtained at an optimal target power of 500 W and an optimal deposition pressure of 2 mTorr with high saturation flux density, B sat Ͼ 2.4 T, and low easy-axis coercivity, H ce ഛ 15 Oe, and hard-axis coercivity, H ch ഛ 3 Oe, at a film thickness of 2000 Å. While the magnetostriction remains at ϳ4 ϫ 10 −6 the stress was further optimized by applying substrate bias at a controlled level ഛ50 V without sacrificing film magnetic softness.
In this work, interlayer exchange coupling fields of spin valve samples have been measured as a function of temperature, and fit to a temperature dependent combination of RKKY and Neel coupling fields. The RKKY coupling strength is assumed proportional to the form (T/T0)/sinh(T/T0), where T is temperature and T0 is characteristic temperature. [N. Persat and A. Dinia, Phys. Rev. B 56, 2676 (1997)] This allows the RKKY coupling and Neel coupling field to be separated quantitatively. The results of such an analysis on various CoFe/Cu/CoFe spin valve structures allow the extraction of a roughness parameter from the Neel model and the T0 parameter from the RKKY model. The measured roughness on the top surface was generally 2–3 times greater than the value obtained from the Neel analysis. The extracted T0 parameter was one order of magnitude smaller than that measured for bulk Cu by the de Hass–van Alphen effect. [N. Persat and A. Dinia, Phys. Rev. B. 56, 2676 (1997); B. Lengeler and W. R. Wampler, Phys. Rev. B 15, 5493 (1977)] Part of this reduction may be due to the 2D nature of the electron gas, as justified by an estimate of the 2D free electron Fermi energy calculation. However a factor of four difference remains, with the experimental value of T0 being around 100 K. This behavior, while not fully explained, is consistent with the measurements of other workers.
In this article, we present data on the critical dependence of the magnetic, electrical and microstructural properties of spin-valves (SV) on seed-layer thicknesses. The SV structure is: seed-layer/PtMn 140 A/CoFe 16 A/Ru 8.5 A/CoFe 21 A/Cu 20 A/CoFe 12 A/NiFe 30 A/Ta 30 A, where the seed layer is NiFeCr-CoFe or NiFeCr/NiFe. As the thickness of the bilayer seed layer is varied, it is found that a critical thickness boundary exists across which the film properties are radically different. The GMR ratio increased from 7% to 14% (a 100% change), the sheet resistance decreased by about 4 ohms/square and the crystalline texture transitioned from weak to extremely strong (111) texture. The critical thickness boundary is at a combined thickness of 37 A to 40 A. These results suggest a mechanism at the boundary between NiFeCr and CoFe during film growth. A better lattice match between NiFeCr-CoFe, for example, NiFeCr 33 A and CoFe 7 A, generates a strong (111) texture, which enhances the MR% as compared to NiFeCr 33 A/CoFe 6 A. The H 50 (the field at 50% MR) also exceeds 2000 Oe. This also indicates enhancement of the PtMn fcc to fct transition based on the specifically combined thicknesses of NiFeCr-CoFe. With the NiFeCr-NiFe seed layer, the critical thickness effect is not observed within these thickness ranges.
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